JMA Seismic Intensity Research Articles

Reconnaissance report on geotechnical damage caused by an earthquake with JMA seismic intensity 7 twice in 28 h, Kumamoto, Japan

An earthquake with magnitude 6.5 occurred at 21:26 p.m. on April 14, 2016 with its epicenter (N: 32°42'00'' E: 130°48'00'') near the Aso Kumamoto airport (4km northeast of Mashiki), at a focal depth of approximately 10km. The second earthquake (M7.3) occurred at 1:25a.m. on April 16, 2016 with the epicenter (N: 32°48'00'', E: 130°48'00'') at a focal depth of 12km. These earthquakes were caused by two active faults: the Futagawa and Hinagu faults. These two seismic events are referred to as the 2016 Kumamoto Earthquake. This was the fourth earthquake with seismic intensity of 7 ever recorded in Japan. The Kumamoto prefecture was severely and locally damaged by the earthquakes, feeling strong seismic activity twice in 28h. In particular, the second earthquake triggered landslides, rock falls, wide area liquefaction, and ground fissures. As of May 20, 2016, over 1500 aftershocks have occurred. An active fault with ground fissures and complex deformation of the ground was observed around Nishihara, Mashiki, Kashima, Mifune, south Kumamoto, and Kousa along the Futagawa and Hinagu fault zones. Meanwhile, many slope failures and landslides occurred in Aso. Despite only mild rain, a significant slope failure destroyed the Aso-ohashi bridge, and shut down national route R57; leading to severe destruction in and around Mashiki, Nishihara, and Aso, the most populous area in the Kumamoto prefecture.After the foreshock on April 14, the Japan Geotechnical Society (JGS) organized an investigation team to support the recovery of the damaged sites and to study the potential of secondary disasters. The JGS worked quickly to conduct diagnostic investigations of a river dike for slope failures and landslides should there be heavy rainfall. The investigation team consisted of 9 sub-groups: (1) active fault and earthquake motion, (2) geo-disasters, such as slope failures, debris flow, and landslides, (3) liquefaction, subsidence, and port damage, (4) river dikes and dams, (5) disaster waste, (6) road, retaining walls, and earth reinforced structures, (7) historical heritage, (8) oita, and (9) southern Kyusyu. Since the 2011 Tohoku Earthquake off the Pacific Coast, an attempt has been made to recycle disaster waste as construction material. Hence, this investigation team also involves a subgroup for investigation of disaster waste. This reconnaissance report introduces the geological features in the Kumamoto prefecture, discusses the 2016 Kumamoto earthquake, and then summarizes results reported by subgroups 1–5. All results reported in this paper were obtained from April 14 to June 16, 2016.

SEISMIC COLLAPSING ANALYSIS OF ONE-STORY WOODEN KINDERGARTEN STRUCTURE AGAINST STRONG EARTHQUAKE GROUND MOTION

3-D collapsing process analysis of an old Japanese-style one-story wooden structure under two strong earthquake ground motions with a seismic intensity level was car-ried out in order to investigate the seismic performance of this one-story wooden structure without/with seismic retrofit. As a result, this wooden structure collapsed against a strong earthquake ground motion with the JMA seismic intensity “6 upper” level.

震度と震度継続時間の一貫した経験的予測体系の提案

震度と震度継続時間の一貫した経験的予測体系の提案

SEISMIC COLLAPSING ANALYSIS OF THREE-STORY WOODEN HOTEL

A 3-D collapsing-process analysis of an old Japanese-style 3-story wooden hotel under strong earthquake ground motions was carried out with three seismic intensity levels to investigate its seismic performance. Three earthquake ground motions were evaluated from three ground boring data around this wooden hotel, using the non-linear amplification characteristics of surface soil layer above the engineering base rock. As a result, this wooden hotel collapsed against a strong earthquake ground motion with JMA seismic intensity of a “6 upper” level.

観測震度または予測震度を与件とする震度継続時間の条件付予測式

本研究は、震度継続時間を予測する簡便手法の確立を目的として、観測震度または予測震度を与件とした条件付予測式を提案するものである。1996～2013年の主要な35地震（Mw =5.0～9.0）で観測された約1万の3成分の加速度記録を用いて、震度閾値（震度階1～6強の8 種類）を上回る震度継続時間を計測し、観測震度と着目する震度閾値との震度差、断層最短距離、モーメントマグニチュード、着目地点における平均S波速度、Vs=1400m層上面深度、地震タイプ（内陸地殻内、プレート境界、プレート内）を説明変数とする予測モデルを構築した。震度予測を外生化することで、常用対数標準偏差0.2以下と精度が高く、震度継続時間1～300秒程度の広いレンジを対象とした予測式が得られた。

Exposure Analysis Using the Probabilistic Seismic Hazard Maps for Japan

With the aim of better understanding and more effective utilization of probabilistic seismic hazard maps in Japan, exposure analysis has been carried out by combining hazard maps with population distribution maps. Approximately 80% of the population of Japan is exposed to a relatively high seismic hazard, i.e., a 3% probability of exceeding JMAseismic intensity 6 lower within 30 years. In highly populated areas, specifically in major metropolitan areas, seismic hazard tends to relatively high because of the site amplification effects of holocene deposits. In implementing earthquake disaster mitigation measures, it is important to consider the overlapping effect of seismic hazard and demographic distributions.

高強度鋼を用いた構造システムの実大静的載荷試験による性能検証

This paper summarizes the results of static loading tests conducted for a full-scale, four-storied frame structure. The structure was composed of high-strength steel, H-SA700, and designed based on the separately proposed performance-based method intending damage-free structures even under extreme earthquakes. Loading history, in a form of enforced displacement at each story, was determined through response analyses. Test results showed that the structure would remain elastic under earthquakes of JMA seismic intensity 7, indicating the adequacy of the design method. Reusability of the structural components was also confirmed by visual and dimensional checking.

2011 年東北地方太平洋沖地震における最大加速度、計測震度と地震動スペクトルの関係

2011 年東北地方太平洋沖地震における最大加速度、計測震度と地震動スペクトルの関係

STUDY ON DAMAGE OF COMPANIES CAUSED BY THE 2011 OFF THE PACIFIC COAST OF TOHOKU EARTHQUAKE

Information on damage of companies caused by the 2011 off the Pacific coast of Tohoku earthquake was collected by the use of released information, and the relations between the damage and JMA seismic intensity scales of the company location points were studied. The damage ratios to buildings and facilities increase with the higher JMA seismic intensity scale. Due to the tsunami damage, companies located in the coast areas such as material, energy, life and medical industries needed more recovery days than other companies in the inland areas such as electric, information, automobile, and machinery industries.

計測震度のフィルタを修正することによって建物被害率と対応させる試み

計測震度のフィルタを修正することによって建物被害率と対応させる試み

EXPERIMENTAL STUDY ON LATERAL BUCKLING BEHAVIOR OF WELD-FREE BUILT-UP MEMBER MADE OF H-SA700A HIGH-STRENGTH STEEL

Researchers, including the authors of this paper, are striving to develop main members of built-up structures using 780N/mm2 high-strength steel for a new built-up structural system that prevents buildings from collapsing or being damaged by a severe earthquake (JMA seismic intensity 6.5) and enables rapid functional recovery. The authors propose a weld-free built-up structural member that has a cross section of two channel steel members made of high-strength steel stitched together with bolts. This member has high strength, so that its cross section can be small and it becomes slender, thus creating the possibility of buckling problems.In this study, lateral-torsional buckling tests were conducted on beams with various stitching bolt pitch under uniform bending moment and bending moment gradient along the member axis. Then, a calculation formula for the flexural strength was presented. The values of the flexural strength obtained from calculation were compared with those obtained from the lateral-torsional buckling tests. As the long distance between the supporting points was required for the elastic lateral-torsional buckling tests, a new loading apparatus was fabricated. Precision, supporting conditions, and loading conditions of the apparatus were verified before the experiments. These results show that:1) Although a twist angle appeared from an early stage, the initial stiffness remained substantially unchanged in the relationship between the bending moment M and the support point twist angle.2) When the bolt pitch was increased, the lateral buckling strength was reduced. The effect produced by the stitching bolt pitch on the lateral buckling strength was relatively large.3) If the bolt pitch remained within the range from 200mm to 800mm, the calculated values of lateral buckling were almost same as the experimental values for both cases of uniform bending moment and linearly changing bending moment.

ON ELASTIC LATERAL BUCKLING STRENGTH FORMULA FOR WELD-FREE BUILT-UP MEMBER MADE OF H-SA700A HIGH-STRENGTH STEEL

Researchers, including the authors of this paper, are striving to develop main members of built-up structures using 780N/mm2 high-strength steel for a new built-up structural system that prevents buildings from collapsing or being damaged by a severe earthquake (JMA seismic intensity 6.5) and enables rapid functional recovery.The authors propose a weld-free built-up structural member that has a cross section of two channel steel members made of high-strength steel stitched together with bolts. This member has high strength, so that its cross section can be small and it becomes slender, thus creating the possibility of buckling problems.In a previous study, an elastic lateral-torsional buckling test was carried out on such members, and a simple flexural strength formula was presented for practical design. The value calculated by this fromula is safe compared with the lateral-torsional buckling test results. However, it cannot represent the influence of bolt pitch and is not accurate enough for design.The sectional shape of the member is changed in the longitudial direction, so a new torsion constatnt calculation equation is required. This paper presents a precise calculation equation for torsion and warping constants of this member and derives an elastic lateral buckling strength formula. The accuracy and efficiency of this formula are demonstrated by a comparative study using lateral-torsional buckling tests and axial buckling and twisting test results.

地盤条件を考慮した地震による鉄道構造物の被害関数の構築

The damage survey data of railway structures in the 1978 Miyagi-ken Oki earthquake, the 1995 Hyogo-ken Nanbu earthquake, and the 2004 Niigata-ken Chuetsu earthquake are collected and compiled. The seismic vulnerability functions of railway structures for different geomorphologic conditions are constructed in the range of the JMA seismic intensity 4 to 7. The results indicate that the railway structure damage appears from the JMA seismic intensity 5+ and that the damage is higher at mountain, hill or valley plane.

ACTUAL CONCRETE STRENGTH AND SEISMIC DAMAGE PREDICTION OF EXISTING REINFORCED CONCRETE BUILDINGS IN HOKKAIDO BASED ON SEISMIC DIAGNOSIS

In this paper, we investigate the seismic performance of existing reinforced concrete buildings, the damage prediction and the actual concrete strength based on the seismic diagnosis results from 1996 to 2006 in Hokkaido. The following conclusions are obtained: (1) 79% of buildings built before 1971 do not satisfy the sesmic capacity index Is≥0.6; (2) The average ratio of actual concrete strength by core tests to design basis one is 1.39; (3) The seismic retrofit of buildings reduces the predicted seismic damage ratio over moderate damage rank to approximately one fourth as compared to the non-retrofit buildings under the earthquake ground motion level of JMA seismic intensity of 6.

２００７年新潟県中越沖地震における生産施設の機能被害とその要因分析

We conducted a questionnaire survey on damage of industrial facilities during the 2007 Niigataken Chuetsu-oki Earthquake to examine the relationship between seismic intensity and damage of facilities. We also investigated the cause of functional damage comparing a period of restoration of various damaged parts to those of functional cessation. The following conclusions are obtained. 1) In the JMA seismic intensity over 5.5, various damage were occurred in many parts of facilities. Some facilities have shut down for a week or more. 2) The factor related to functional cessation varied corresponding to requirements for performance of the facility.

震度のリアルタイム演算法

A new calculation method is proposed for a real-time seismic intensity indicator (Ir), whose concept is similarly to the JMA seismic intensity (IJMA)defined by Japan Meteorological Agency. With the increasing requirements of earthquake early warning (EEW) system, it is much more obvious that IJMA has a real-time delay since the IJMA needs a filtering operation in frequency domain. In order to improve the real-time calculation suitable for the EEW system, a new real-time seismic intensity indicator, Ir (real-time seismic intensity), is defined by using an approximating filter in time domain instead of the original filter in frequency domain. This indicator, Ir,can be calculated as a time series on real-time and its maximum value, Ia (approximate seismic intensity), corresponds to an approximate value of IJMA. The relationships between IJMA and Ia value are examined by means of using a large number of strong motion records. Results show that Ia value estimates IJMA with reasonable accuracy in wide intensity ranges. For a small computing system like a strong-motion seismograph, it is easier to process Ir than processing IJMA. Therefore, Ir is suitable for using in an EEW system based on the concept of JMA seismic intensity.

新潟県中越沖地震による海岸港湾施設の被害および海底古木による漁業被害の現地調査

A field investigation has been carried out to investigate the damage of coastal, port and harbour facilities caused by the Niigataken Chuetsu-oki Earthquake in 2007. The instrumental JMA seismic intensity of a strong 6 was registered in Kariwa village, Kashiwazaki and Nagaoka cities, in Niigata, Japan. The damages to coastal, port and harbour facilities were investigated. The old seawalls at Osaki coast in Kashiwazaki were broken due to strong seismic motions. Several coastal facilities ware partly broken due to liquefaction occurred by the severe ground shaking. The corners of concrete caissons used for a breakwater were broken off due to strong collisions. There are many old woods appeared on a sea bottom surface after the earthquake in the region offshore from Izumozaki town to Kashiwazaki city. The woods might appear to floating up to the sea bottom surface due to the liquefaction of sea bottom sediments.

2地点の計測震度と微動H/Vおよび地形・地質分類を利用した面的震度分布の即時推定

地震発生時に詳細な震度分布を即時的に把握することは，災害発生時の初動計画において重要なことである。また，行政による公助だけでなく，地域住民自身による自助，共助を考えるうえで，市区町村内の詳細な震度分布は重要な情報となるであろう。 兵庫県南部地震以降，日本全国に数多くの地震観測点が設置され，地震発生直後に各地の震度が速報されるようになった。これらの地震計は日本全国，もしくは，都道府県内の震度分布を把握するのに十分な密度で設置されている。 しかし，地域住民の視点で考えると，すなわち，市区町村内のより詳細な震度分布を把握するには十分な地震観測点密度であるとはいえない。横浜市のような特別な場合を除き，多くの市区町村に設置されている地震観測点は1地点から数点であろう。 そこで，本論では，ニューラルネットワークによる情報処理を応用し，2地点の地震観測点で観測された計測震度から面的な震度分布を即時的に推定する方法を提案した。提案手法を高密度地震観測網が設置されている横浜市において適用した結果，良好な精度で震度分布を推定することができた。また，学習に用いる地震数や観測点数が推定精度に与える影響についても検討した。

耐震補強推進協議会による地域ぐるみの建物耐震化推進運動

In 2006, the Tokyo Metropolitan Disaster Management Council revised the estimation of major damage in the eastern wards of Tokyo metropolis for an earthquake beneath northern Tokyo Bay (M7.3) with a JMA seismic intensity of scale 6 upper. It is assumed that 12, 337 houses in Sumida City would collapse completely. The number of wooden dwelling houses built before 1981 adopting the old seismic code totals 21, 898 in Sumida City, of which 6, 863 are located in the most dangerous area with a high density of wooden dwelling houses. Seismic retrofitting of these houses is urgently needed. This paper reports on the countermeasures planned by Sumida City.Sumida City has designed a support program for safe living spaces, which promotes antiseismic performance checks and seismic retrofits. A financial support system for retrofitting provided by Sumida City began in January 2006, and this system is characterized by dividing seismic retrofits into easy retrofits and regular ones, with application to residents of rental housing. The Sumida Anti-seismic Reinforcement Forum 2006 was held in February 2006 to announce this system. Moreover, the Sumida Quakeproof Reinforcement Promotion Conference, which exercises governance involving inhabitants, companies, and local government, was organized in June 2006. This conference is now campaigning for seismic retrofits through meetings held at every community center of each community in the city.

建築物の耐震改修促進法改正と政策の展開

The Building Standards Act was enacted in 1950 to promote safe buildings in Japan. In 1981, the seismic code was largely revised, requiring that buildings would not collapse, causing casualties, under a JMA seismic intensity of scale 6 upper. Buildings built before 1981 adopting the old seismic code but not the new one are classed as “existing non-conforming buildings”. These buildings do not conform to the new seismic code, however, damage to buildings built before 1981 caused by the Great Hanshin-Awaji Earthquake in 1995 was much greater than that to buildings constructed after 1981. This resulted in the enactment of Building Retrofitting Promotion Act in 1995, which aims to promote anti-seismic performance checks and seismic retrofits.This paper shows the situation of current retrofitting and policy development. It indicates the situation of administrative guidance to owners of about 90, 000 specific buildings not constructed to an anti-seismic design. It is significant to promote seismic retrofits for houses that constitute the majority of buildings. In 2003, the total number of houses was estimated to be about 47, 000, 000, of which about 18, 500, 000 were built before 1980. 11, 500, 000 of these are estimated to be vulnerable to earthquakes. As a policy development, the target is to increase the current seismic retrofit rate of 75% to 90% by 2015. To achieve this, the Building Retrofitting Promotion Act has been amended, and retrofitting is being promoted by local governments, strengthening administrative guidance to owners of specific buildings, providing support and financing for seismic retrofits, as well as support through the tax system.